This invention is directed to a voltage compensating drive circuit for a thermal printer and, in particular, to a voltage compensating drive circuit for controlling the duration of current driving pulses applied to exothermic elements in response to changes in the magnitude of the supply voltage to thereby stabilize the printing density of the print characters recorded on a thermally sensitive medium.
Although thermal printers and thermal printing selection circuitry therefor have been known in the printing art for many years, thermal printers have not gained wide commercial use and acceptance. One reason for this is variations in the supply voltage that result in the print characters recorded on thermally sensitive print mediums having an unstable printing density. This is particularly the case when a limited power supply, such as a DC battery, is utilized in a small-sized thermal printer. Accordingly, a voltage compensation driving circuit that would stabilize the printing density of the print characters recorded on a thermally sensitive medium would eliminate the disadvantage noted above.